Question

Which weak acid would be best to use when preparing a buffer
solution with a pH of 8.70?
An acid with Ka = 1.3 × 10-10
An acid with Ka = 2.1 × 10-9
An acid with Ka = 2.5 × 10-5
An acid with Ka = 4.0 × 10-6
An acid with Ka = 3.2 × 10-7
An acid with Ka = 3.2 × 10-4